My early silver dot tach did not work at all once I installed a hyfire ignition box. This is caused by the fact that the stock tack is looking for a high voltage signal that no longer exist. I was able to modify the tach to run off of the Hyfire's tach port by placing a jumper over the initial signal resister. As a side note I experimented with the hyfire's tach testor and found that the stock tach is pretty acurate.

that's great.

I could never get mine to work and just went with an autometer. Does the old tach still bounce around alot? I kind of got used to the dead steady new tach but I would go back to the original unit if it worked OK.

my hero!!!!

need to do tis ASAP

hmmm... mine looks different....
could be because it is a 912 tach

ill open up a 914 one too...

synthesisdv, it still bounces around like a squirrel in the middle of the road. That could probably be cured by place a capacitor across the needle leads but I didn't think to try it. It's kind of tough to see what is happening on the circuit board because it wraps around the needle mechanism.

hey dean,

you seem to know your way around a circuit board. How hard do you think it would be to transplant the guts of my autometer into the silver dot porsche tach?

I wouldn't want to do it if I couldn't use the silver dot needle.

I don't think I will ever go back to stock tach. Love my Autometer and the shift light.
I can see the light out of the corner of my peripherial vision while screaming though the cones. set it go go on at 5800 RPM I find I am staying off the rev limiter and shifting to 3rd earlier pulling WAY harder to the next feature.
Pretty cool to be able to fix the stock one though

ill be doing this on friday.

i didnt know the hyfire had a tach testor....

Okay, for the benefit of those of us who have never disassembled gauges, could someone describe how to disassemble a VDO tach. I assume disassembly is from the gauge face side?

I think I could handle soldering the jumper around the resistor, but I just don't want to ruin the gauge taking it apart. Thanks.

QUOTE (maf914 @ Apr 11 2005, 10:05 AM)

Okay, for the benefit of those of us who have never disassembled gauges, could someone describe how to disassemble a VDO tach. I assume disassembly is from the gauge face side? I think I could handle soldering the jumper around the resistor, but I just don't want to ruin the gauge taking it apart. Thanks.

uncrimp the bezel...a royal PITA.

then take the 3 or 4 screws out from the back. voila..... done.